1. Field of the Invention
The present invention relates to a process for producing a flexible polyurethane foam having improved flame retardance and physical properties.
2. Description of the Prior Art
Flexible polyurethane foams have long been in use in a great variety of application fields on account of their characteristic properties. A disadvantage of flexible polyurethane foams is that they have tendency to burn. Therefore, they are subject to regulations for flame retardance, and recently, the regulations are becoming more and more stringent. Rendering polyurethane foams flame retardancy is a very important technical subject.
There have been proposed many technologies for rendering polyurethane foams flame retardancy. Among the most popular, is the proposal of the incorporation of a phosphorus-containing halogen compound (such as tri (.beta.-chloroethyl)phosphate and "Thermorin 101"), as the flame retardant. However, this method is appropriate only when the foam contains more than about 1 wt % of phosphorus. This means that it is necessary to add 10-30 parts by weight of expensive phosphorus/halogen-based flame retardant to 100 parts by weight of polyhydroxy compound. The resulting polyurethane foam is considerably more expensive as a matter of course. Another disadvantage of this method is that the phosphorus/halogen-based flame retardant exhibits a plasticizing effect, thereby adversely affecting the foam properties (e.g., lowering the hardness and tensile strength of foams and increasing the permanent set of foams). In addition, the flame retardant vaporizes and disappears with the lapse of time when foams are used at high temperatures. Not only does this lead to a decrease in flame-retardant performance but this also causes the contamination of nearby machines and equipment. Moreover, polyurethane foams incorporated with a phosphorus/halogen-based flame retardant corrode metals (such as iron and aluminum) in contact with them during use.
Rendering polyurethane foams flame retardant by incorporating these foams with a phosphorus- and halogen-containing compound as a flame retardant, presents many problems as mentioned above. Therefore, there has been a strong demand for the development of a new technology for improving the flame retardance of polyurethane foams.